Improving the efficiency of wastewater sludge pretreatment by high temperature hydrolysis before digestion

Summary

The results of investigating activated sludge and primary sludge thermal pretreatment with the purpose of improving the efficiency of anaerobic digestion are presented. The highest efficiency of activated sludge organics transfer into readily soluble form is ensured after thermal hydrolysis at 160°C. The solubility of primary sludge organic matter increases evenly with the temperature increase in the range of 100–200 °С. The maximum biogas output in the ultimate digestion test is increasing after activated sludge hydrolysis at 160°С, primary sludge hydrolysis – at 180–200°С. Digestion in a continuous mode after activated sludge pretreatment at 140–160 °С results in 53% gas generation increase. Any further hydrolysis temperature increase produces a negative impact on gas generation and disintegration of activated sludge ashless matter. Thermal hydrolysis of primary sludge in thermophilic mode is not efficient. Pretreated sludge dewatering performance is improved; consequently the flocculant dosage can be reduced by 0.8–1.0 kg/t DS.